code: def __len__(self):
      return len(self.ctx)
  
file_path: DeepKE/example/llm/CPM-Bee/src/cpm_live/training_tasks/ant/pretrain.py
imports: import torch.utils.data
  import random
  import numpy
label_desc: Use image node_id 2 for calling the CPMAntPretrainDataset obj's underlying member method code with example usage: obj.__len__() and returns: len